1. Field of the Invention
This invention relates to the field of elastic couplings, or joints which utilize an elastomer link between two rigid, coaxial elements, making possible their relative rotation, without friction, around an axis on which significant radial loads and axial forces can be exerted, while ensuring controlled filtering rigidities by means of a joint which is easy to manufacture. The invention relates, in particular, to the articulation of suspension arms for motor vehicles, as well as to the antivibration suspension of sensitive mobile or stationary equipment.
2. Description of the Prior Art
The articulation, by rotation of an arm, e.g. a suspension arm, on a flange fixed to the chassis of a vehicle, usually makes use of the deformation of an elastomer based elastic block.
The refinements of conventional elastic couplings, such as those described in Great Britain Patent No. 637,901 to Silentbloc, French Patent No. 957,174 and French Patent No. 1.415.871 to Metalastik have become inadequate in relation to current industrial requirements, particularly in relation to the requirements of the automobile industry. They were first concerned with improving the capabilities for angular movement, without play, by introducing the ability to slide beyond a certain friction limit. French Patent No. 2,430,538 to SAGA, for a swivel bearing and European Patent No. 0,163,980 (equivalent to U.S. Pat. No. 4,671,694) to Boge and TRW-Ehrenreich for a quasi-cylindrical sleeve, disclose the use of axial prestressing of the elastic portion of the sleeve by conical deformation of the extremities of the external tubular ring, which extremities are folded toward the inside of the ring. As a result of this prestress, the angular movement must exceed a certain threshold to utilize the functional sliding of the joint. The latter two documents discussed above also disclose articulations wherein a major axial force can be exerted, without the possibility of play, but which always show a high rigidity connection, which connection cannot then claim to provide good antivibration filtering.
On the other hand, French Patent No. 827,020 to Metalastik discloses the possibility of axial play with good filtering by means of the use of a layer of rubber located exterior to the external armature. This layer of rubber thereby acts as a stop to ensure reaction to axial forces after the closing of a gap, thereby not permitting the simultaneous filtering and opposition to axial forces.
For radial filtering, refinements running in another direction improve the filtering by reducing the radial rigidity over a short stroke limited by the activation of a stop, to a position which is as close as possible to the functional position.
European Patent No. 0,162,745 to Hutch discloses the utilization of grooves worked into the exposed lateral surface of the elastic material. These grooves close to ensure a stop function by mechanical contact between their walls, and also to allow for major radial forces to be exerted beyond the filtering zone made possible by the short stroke. Axial forces may not be applied to this type of part in particular, and in addition, the "conical" orientation, i.e. an angular difference between the coaxial elements, modifies the value of the functional play by restricting it to the point where it is eliminated altogether beyond a certain angle.
An improvement of this device is disclosed in French Patent No. 2,650,040 to Caoutchouc Manufacture et Plastiques, the present applicant. This patent describes an elastic joint having a significant radial filtering capability and gradual stroke limitation, by contact with a large cell surface, worked into a cylindrical housing, while maintaining an axial prestress between the adherized conical washers. The high form factor, which is favorable on account of the adherization of the washers, makes it possible to use a significant quantity of resilient material, which thereby retains its filtering capabilities, while also retaining the ability to accept large forces in the axial direction.
This arrangement retains the capabilities of so-called "conical" angular movement between the axes of the components. But these latter two applications, which are quite different, do not have as their primary objective a good axial filtering which is compatible with occasional, but large, axial forces.
Apparently, a requirement for axial filtering, while retaining the capability of bearing large axial forces, is not satisfied in the devices of the prior art except by separating the functions, which separate functions require the user to separately adjust the effective filtering and to limit the stroke by means of additional appropriate stops.